Olefin isomerization



United States Pate 3,384,677 GLENN ESGMEREZATEQN Raymond A. Franz, Kirkwood, and James C. Hill, St. Louis, Mo., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Feb. 5, 1964, er. No. 342,807 18 Claims. (Cl. 260683.2)

The present invention relates to a process for the conversion of hydrocarbons. More particularly, the present invention relates to a process for the isomerization of internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons.

Recently, it has been found that straight-chain internally unsaturated mono-olefin hydrocarbons may be isomerized to the corresponding straight-chain terminally unsaturated mono-olefin hydrocarbons by reacting internally unsaturated mono-olefin hydrocarbons with di-alkyl aluminum hydride to form n-tri-alkyl aluminum which is then pyrolyzed to yield terminally unsaturated straightchain mono-olefin hydrocarbons. This isomerization method comprises dispersing a di-alkyl aluminum hydride in straight-chain monoolefin hydrocarbons and subjecting the mixture to temperatures of 150 C. and greater to form n-tri-alkyl aluminum. The n-tri-alkyl aluminum or pyrolysis yields terminally unsaturated mono-olefin hydrocarbons. In this isomerization process, the internally unsaturated mono-olefins are used in a quantity such as to serve both as a reactant and as a solvent for the reaction. Though this proces provides a new and useful method for the isomerization of internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons, the yields of terminally unsaturated mono-olefin hydrocarbon have been somewhat unsatisfactory by this process.

It is an object of the present invention to provide a new and improved process for the conversion of hydrocarbons. Another object of the present invention is to provide a new and improved process for the isomerization of unsaturated hydrocarbons. Still another object of the present invention is to provide a new and improved process for the isomerization of internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons. Additional objects will become apparent from the following description of the invention herein disclosed.

The present invention, which fulfills these and other objects, comprises intimately co-mixing a reactive alkyl aluminum selected from the group consisting of tri-alkyl aluminum and alkyl aluminum hydrides with internally unsaturated mono-olefin hydrocarbons at elevated temperatures until alkylation with said internally unsaturated mono-olefin hydrocarbons is complete and then subjecting the resulting tri-alkyl aluminum, While in the presence of a solvent selected from the group consisting of ethers and tertiary amines, to conditions such as to decompose the tri-alkyl aluminum to the corresponding di-alkyl aluminum hydride and recovering terminally unsaturated mono-olefin hydrocarbons as a decomposition product. The present invention provides two very significant improvements over the prior art. First, the yield of terminally unsaturated mono-olefin hydrocarbons is substantially increased. A second advantage is found in the fact that the present invention has utility for the isomerization of branched-chain internally unsaturated monoolefin hydrocarbons as Well as straight-chain internally unsaturated mono-olefin hydrocarbons to terminally unsaturated mono-olefin hydrocarbons.

The first step of the present invention, herein referred to as the alkylation step, comprises intimately mixing an alkyl aluminum and an internally unsaturated monoolefin hydrocarbon feed. The conditions of this first step "ice are such that the alkyl aluminum is alkylated to a trialkyl aluminum having the same number of carbon atoms per alkyl substituent as are in the internally unsaturated mono-olefin hydrocarbons in the feed. It is presently believed that it is at this point that isonierization occurs, either at or during the time the internally unsaturated mono-olefin hydrocarbon is alkylated onto the alkyl aluminum. However, the present invention is not to be limited to any particular theory as to how or when isomerization takes place, but only to the mechanics for carrying out the isomerization. The alkylation step may be carried out in the presence of the ether and tertiary amine solvents of the present invention which are hereinbelow described. Alkylation also may be carried out without the use of solvents using only the reactants. A useful method of alkylation comprises carrying out the alkylation reaction in the presence of a saturated hydrocarbon as disclosed and claimed in co-pen-ding application Ser. No. 334,918.

After alkylation is complete, the second step, herein referred to as the decomposition step, is initiated. Decomposition comprises subjecting the solution of tri-alkyl aluminum formed in the alkylation step in a solvent selected from the group consisting of an ether and a tertiary amine to conditions such as to decompose the tri-alkyl aluminum back to the corresponding di-alkyl aluminum hydride and recovering the alkyl group thereby liberated from the tri-alkyl aluminum, the alkyl group providing the terminally unsaturated product of the present invention.

Though both alitylation and decomposition may be carried out in the presence of the solvents described here in, the present invention is not to be so limited since it is within the scope of the present invention that different solvents be used in each of the two steps of the present invention, it being essential only that the solvents of the present invention be used in the decomposition step.

In order to further describe and to illustrate the present invention, the following examples are presented. These examples are not to be construed as limiting the present invention in any manner.

EXAMPLE I Approximately 23.4 grams of tri-isobutyl aluminum were admixed with 67 grams of hexene-2. During the reaction of hexene-2- and tri-isobutyl aluminum, a temperature of to C. and a pressure of 105 p.s.i.g. were maintained. There was a continuous evolution of isobutenes from the reaction mass. After approximately 10 hours, the alkylation reaction was stopped. The pressure was then reduced to atmospheric pressure and unreacted hexenes distilled from the reaction mass. The resulting trim-hexyl aluminum was decomposed by dispersing approximately 8.4 grams of this material in about 4.7 grams of dimethyl ether of ethylene glycol. Next, the pressure was reduced to 30 mm. Hg and the temperature raised to C. In this manner the tri-n-hexyl aluminum was decomposed back to the di-n-hexyl aluminum hydride and the resulting hexyl groups recovered as an overhead product of the decomposition. This overhead product represented a conversion of 73 percent and was found to contain 2 percent by weight-n-hexane and 98 percent by weight hexene-l.

EXAMPLE Ii Example I was substantially repeated with the exception that none of the solvents of the present invention were used in the alkylation or decomposition steps and the temperature during decomposition was 135 C. The resulting overhead decomposition product represented a conversion of 62.5 percent and was found to contain 10 percent by weight n-hexane, 82 percent by weight hexene- 1 and 8 percent by weight hexene-Z.

Comparison of the results of Examples I and H is believed to clearly demonstrate the improved and unexpected results obtainable through use of the present lnvention.

EXAMPLE III The procedure of Example I is substantially repeated with the exception that the solvent used in the decomposition step is triethylarnine. A good conversion and high yield of terminally unsaturated mono-olefin hydrocarbons are obtained.

The solvents useful in the present invention are others and tertiary amines. The ethers include alkyl ethers, aryl ethers, alkyl polyethers, aryl polyethers, haloalkyl ethers, haloalkyl polyethers, haloaryl polyethers, alkyl and aryl thioethers and the like. Also, the cyclic ethers are useful as solvents in the present invention. In those ethers containing alkyl radicals, the alkyl radical may be a saturated radical or an ethylenically unsaturated radical. The alkyl and/ or aryl radicals of the ethers will usually contain 1 to carbon atoms per radical. Representative of ethers within the scope of the present invention are dibenzyl ether, methoxy benzene, ethoxy benzene, hexyl ether, pentyl ether, butyl ether, propoxy benzene, dimethoxy benzenes, phenyl benzyl ether, methylbutyl ethers, methoxy ethoxy benzenes, diphenyl ether, chloroethyl ethers, bromethyl ethers, dimethoxy ethanes, dimethoxy ropanes, ethyl thioether, propyl thioether, butyl thioether, benzyl thioether, 1,4-dioxane pyran, dihydropyran, furan, and the like.

The tertiary amines most useful in the present invention are the tri-alkyl amines. Preferably, these tri-alkyl amines are those having 2 to carbon atoms in the alkyl groups. Several non-limiting examples of such compounds are triethylamine, methylethylisobutylamine, tripropylamine, dimethyl-ethylamine, dimethylbutylarnine, tributylarnine, diethylmethylarnine, diethylpropylamine, and the like.

Whether the solvent is an ether or a tertiary amine, it is, generally, one which is at least as high boiling, and is preferably higher boiling, than the mono-olefin hydrocarbons of the feed and the product. Also, the solvent should be sufiiciently high boiling as to remain in the liquid state during the alkylation step if it is used in that step and preferably is one which will remain liquid during the decomposition step.

The amount of the solvent used in the present invention whether used in the decomposition step only or in both the decomposition and alkylation steps is expressed in a molar ratio of solvent to the alkyl aluminum. Usually,

this mole ratio is within the range of 0.1 to moles of solvent per mole of the alkyl aluminum. A preferred mole ratio of solvent to the alkyl aluminum is within the range of 1 to 25 moles of the solvent per mole of the alkyl aluminum.

The allryl aluminum which is alkylated in accordance with the practice of the present invention in order to bring about isomerization of internally unsaturated monoolefin hydrocarbons may be a reactive trialkyl aluminum or an alkyl aluminum hydride. Reactive, as the term is used herein, refers to the ability of the tri-alkyl aluminum or alkyl aluminum hydride to react with the internally unsaturated mono-olefin hydrocarbons to form a tri-alkyl aluminum of which at least two or more of the alkyl substituents are derived from the internally unsaturated mono-olefin hydrocarbons in the feed. If the alkyl aluminum is a tri-alkyl aluminum, the alkyl substituents must be displaceable and replaceable by alkylation with the internally unsaturated mono-olefin hydrocarbon feeds of the present invention under the alkylation conditions herein disclosed. Such a tri-all;yl aluminum usually is one whose alkyl substituents are relatively loosely held and which may be readily displaced by the mono-olefin feeds of the present invention. Generally, tri-alkyl aluminums which have branching at the beta carbon atom are the preferred tri-alkyl aluminurns. By beta carbon atom is meant the second carbon atom from the aluminum atom. A non-limiting example of such a tri-alkyl aluminum is tri-isobutyl aluminum.

The alkyl aluminum hydrides which are useful in the present invention are those which under the alkylation conditions described herein will become completely alkylated with the internally unsaturated mono-olefin hydrocarbon feeds of the present invention when in contact with such feeds. Because of the relative instability of alkyl aluminum di-hydrides, such alkyl aluminums are seldom used. The alkyl aluminum hydride most often used in the practice of the present invention is a di-alkyl aluminum hydride. The preferred di-alkyl aluminum hydride is usually one having the same number of carbon atoms per alkyl substituent as are in the interally unsaturated mono-olefin hydrocarbons of the feed. In most instances, the di-alkyl aluminum hydride is obtained by decomposing tri-alkyl aluminum. Once the present invention has undergone one complete cycle including alkylation and decomposition, a di-alkyl aluminum hydride is formed and is the aluminum alkyl used in succeeding cycles regardless of what the initial alkyl aluminum may be. The di-alkyl aluminum resulting from decomposition of the tri-allryl aluminum to produce the terminally unsaturated rnono-olefin hydrocarbons in accordance with the present invention has alkyl substituents having the same number of carbon atoms per substituent as are in the mono-olefins in the feed.

Internally unsaturated mono-olefin hydrocarbons of practically any molecular weight may be isomerized in accordance with the present invention. The internally unsaturated mono-olefin hydrocarbons may have the internal unsaturation at any point in the mono-olefin molecule. For example, both hexene-Z and hexene-3 may be isomerized to hexane-1 by the present invention. Further, the present process is applicable to either straightor branchedchain internally unsaturated mono-olefin hydrocarbons. For example, 4-methylpentene-2 and Z-methylpentene-Z may be isomerized to the corresponding terminally unsaturated mono-olefin hydrocarbons by the process of the present invention. The present invention finds its preferred utility in the isomerization of internally unsaturated monoolefin hy rocarbons of 4 to 20* carbon atoms per molecule.

Generally, in practicing the present invention, the amount of internally unsaturated mono-olefin hydrocarbons used in an amount ranging from one to 15 moles of internally unsaturated mono-olefin hydrocarbon per mole of alkyl aluminum. If it is necessary to both displace and completely replace the alkyl substituents of a tri-alkyl aluminum or a di-alkyl aluminum hydride, then the amount of internally unsaturated mono-olefin hydrocarbon must be adjusted to take into account the necessity of three moles of mono-olefin per mole of alkyl aluminum. However, after the initial cycle of the present process, the alkyl aluminum is generally a di-alkyl aluminum hydride having the same number of carbon atoms per alkyl substituent as are found in the internally unsaturated mono-olefins of the feed. Thus, for the second and all succeedin cycles, only one mole of internally unsaturated mono-olefin hydrocarbon is used per mole of dialkyl aluminum hydride. However, in view of the inability to attain etiiciency in reaction, it is usually preferred to use an excess of the internally unsaturated monoolefin hydrocarbon feed. Preferably, the amount of internally unsaturated mono-olefin hydrocarbon used ranges from that amount which is the stoichiometric equivalent of the aluminum alkyls up to 5 times that amount.

The temperatures at which the alkylation step of the present invention is operated will vary to some extent with the molecular weight of the internally unsaturated monoolefin reactants. Higher temperatures are usually preferred as the molecular weight of the reactants increase. However, the alkylation temperatures seldom are below 100 C. or exceed 400 C. At lower temperatures, the

reactivity between the di-alkyl aluminum hydride and the internally unsaturated mono-olefin hydrocarbon falls below practical standards. At temperatures higher than the above-defined range, decompositions in the system becomes excessive. In the preferred practice of the present invention, the alkylation temperature is most often within the range of from approximately 150 C. to 300 C. preferably 150 C. to 250 C.

Alkylation of the di-alkyl aluminum hydride in accordance with the present invention generally is accomplished at a pressure suflicient to maintain the reactants and the solvent in the liquid state. Such pressures are usually within the range of from approximately atmospheric pressure up to 400 p.s.i.g. and higher. Preferably, pressures of from atmospheric pressure to 300 p.s.i.g. are used in the alkylation step of the present invention.

The length of time necessary for completion of the alkylation step of the present invention will vary depending upon the alkylation conditions and upon the etficiency of the contact between the internally unsaturated monoolefin hydrocarbons and the di-alkyl aluminum hydride. Generally, the time necessary for alkylation will not exceed 24 hours.

Decomposition of the tro-alkyl aluminum hydride to recover the terminally unsaturated mono-olefin hydrocarbons is carried out under conditions whereby the monoolefin products may be dealkylated from the tri-alkyl aluminum without decomposition of the tri-alkyl aluminum further than to a di-alkyl aluminum hydride. Generally, such conditions include the use of stripping agents such as inert gases or light hydrocarbons or, preferably, the use of reduced pressures or a combination of these. In the preferred practice of the present invention, decomposition in accordance with the present invention is carried out at a pressure of 0.1 to 760 mm. Hg and/or while an inert stripping agent, preferably a light hydrocarbon or inert gas such as nitrogen, is being passed through the reaction medium. When reduced pressures are used, the preferred pressures are within the range of from 10 to 100 mm. Hg. If an inert stripping agent is used, it is preferred that it be an inert gas or a non-reactive parafnic hydrocarbon of a lower boiling point than that of the terminally unsaturated mono-olefin hydrocabons being recovered. When an inert stripping gas is used, it is preferred that it be nitrogen.

The temperatures at which decomposition of the trialkyl aluminum is elfected may vary considerably, though will usually not be less than 100 C. or greater than 400 C. Preferably, the decomposition temperatures of the present invention will be within the range of from 150 to 300 C.

The method of recovering the terminally unsaturated mono-olefin hydrocarbons produced by decomposition of the tri-alkyl aluminum formed during alkylation may be any conventional means. Usually, the terminally unsaturated mono-olefin hydrocarbon product is recovered by passing the overhead decomposition product through a condensing medium to condense the terminally unsaturated mono-olefin product as it passes from the reaction system during decomposition. The present invention however, is not to be limited to any particular manner of recovering the terminally unsaturated mono-olefin hydrocarbons produced by the process of the present invention.

The equipment necessary for carrying out the present invention is not critical. It is only required that the equipment as well as its arrangement follow good engineering principles.

What is claimed is:

1. A process for the isomerization of internally unsaturated mono-olefin hydrocarbons which comprises intimately co-mixing a reactive alkyl aluminum selected from the group consisting of tri-alkyl aluminum and alkyl aluminum hydride with internally unsaturated monoolefin hydrocarbons and a solvent selected from the group consisting of ethers and tertiary amines, at elevated temperatures until alkylation with said internally unsaturated mono-olefin hydrocarbons is complete, said solvent being in the liquid phase during said alkylation, subjecting the resulting tri-alkyl aluminum while in the presence of a solvent selected from the group consisting of ethers and tertiary amines to conditions such as to decompose the tri-alkyl aluminum to the corresponding di-alkyl aluminum hydride, and recovering terminally unsaturated mono-olefin hydrocarbons as a decomposition product.

2. The process of claim 1 wherein the internally unsaturated mono-olefin hydrocarbons are straight chain.

3. The process of claim 1 wherein the alkyl aluminum is a tri-alkyl aluminum.

4. The process of claim 3 wherein the tri-alkyl aluminum is a tri-alkyl aluminum in which there is branching on the beta carbon atoms.

5. The process of claim 4 wherein the tri-alkyl aluminum is tri-isobutyl aluminum.

6. The process of claim 1 wherein the alkyl aluminum is intimately co-mixed with the internally unsaturated mono-olefin hydrocarbons at a temperature of to 400 C.

7. The process of claim 1 wherein the pressure at which the alkyl aluminum is intimately co-mixed with the internally unsaturated mono-olefin hydrocarbon is substantially atmospheric pressure.

8. The process of claim 1 wherein the alkyl aluminum is a di-alkyl aluminum hydride.

9. The process of claim 8 wherein the di-alkyl aluminum hydride is one which has the same number of carbon atoms per alkyl substituent as are present in the internally unsaturated mono-olefin hydrocarbon in the feed.

10. The process of claim 1 wherein the internally unsaturated mono-olefin hydrocarbon is branched chain.

11. The process of claim 1 wherein the solvent is an ether selected from the group consisting of alkyl ethers, aryl ethers, alkyl polyethers, aryl polyethers, haloalkyl ethers, haloaryl ethers, haloalkyl polyethers, haloaryl polyethers, alkyl thioethers, aryl thioethers, and cyclic ethers.

12. The process of claim 1 wherein the solvent is a trialkylamine.

13. The process of claim 12 wherein the trialkylamine is one in which the alkyl groups have 2 to 15 carbon atoms.

14. The process of claim 1 wherein the tri-alkyl aluminum is decomposed at a reduced pressure of 0.1 to 760 mm. Hg.

15. The process of claim 1 wherein the tri-alkyl aluminum is decomposed at a temperature of 100 to 400 C.

16. The process of claim 1 wherein the tri-alkyl aluminum is decomposed while passing a stripping agent through the reaction mass.

17. The process of claim 16 wherein the stripping agent is nitrogen.

18. The process of claim 16 wherein the stripping agent is a nonreactive parafiinic hydrocarbon of a boiling point lower than that of the terminally unsaturated mono-olefin hydrocabon.

References Cited UNITED STATES PATENTS 3,282,974 11/1966 Bruno et a1. 260-6832 X 2,906,763 9/ 1959 McKinnis 260-448 2,927,103 3/1960 Schneider et al 260-448 3,015,669 1/ 1962 Ziegler et al 260-448 3,036,016 5/1962 Gordon et al. 252-441 3,163,681 12/ 1964 Gordon et al 260-683.15 3,173,967 3/ 1965 Brown 260-6832 FOREIGN PATENTS 245 ,835 2/ 1961 Australia.

DELBERT E. GANTZ, Primary Examiner.

V. OKEEFE, R. H. SHUBERT, Assistant Examiners. 

1. A PROCESS FOR THE ISOMERIZATION OF INTERNALLY UNSATURATED MONO-OLEFIN HYDROCARBONS WHICH COMPRISES INTIMATELY CO-MIXING A REACTIVE ALKYL ALUMINUM SELECTED FROM THE GROUP CONSISTING OF TRI-ALKYL ALUMINUM AND ALKYL ALUMINUM HYDRIDE WITH INTERNALLY UNSATURATED MONOOLEFIN HYDROCARBONS AND A SOLVENT SELECTED FROM THE GROUP CONSISTING OF ETHERS AND TERTIARY AMINES, AT ELEVATED TEMPERATURES UNTIL ALKYLATION WITH SAID INTERNALLY UNSATURATED MONO-OLEFIN HYDROCARBONS IS COMPLETE, SAID SOLVENT BEING IN THE LIQUID PHASE DURING SAID ALKYLATION, SUBJECTING THE RESULTING TRI-ALKYL ALUMINUM WHILE IN THE PRESENCE OF A SOLVENT SELECTED FROM THE GROUP CONSISTING OF ETHERS AND TERTIARY AMINES TO CONDITIONS SUCH AS TO DECOMPOSE THE TRI-ALKYL ALUMINUM TO THE CORRESPONDING DI-ALKYL ALUMINUM HYDRIDE, AND RECOVERING TERMINALLY UNSATURATED MONO-OLEFIN HYDROCARBONS AS A DECOMPOSITION PRODUCT. 